1. Technical Field
The present invention relates to an image processing device and an image processing method for enlarging a dynamic range by synthesizing a plurality of images acquired by imaging over plural times under different exposure conditions.
2. Related Art
In the field of FA (Factory Automation) and the like, a so-called visual sensor is being put to practical use as a device for optically detecting defects and the like in a half-finished product of the manufacturing process, a product before shipment, and the like, and for optically measuring the size of the defects and the like.
When performing detections and measurements using such a visual sensor, the target needs to be appropriately imaged. The dynamic range (tone range where light can be detected) of the imaging element such as a CCD (Coupled Charged Device) and CMOS (Complementary Metal Oxide Semiconductor) is generally finite. Thus, when the exposure time in time of imaging becomes relatively long, whiteout (halation) entirely or partially occurs, and the luminance and the color information of the target cannot be accurately acquired. When the exposure time in time of imaging becomes relatively short, total underexposure entirely or partially occurs, and an effective luminance cannot be acquired. Furthermore, in the target having portions where the reflectivity locally differs and the target having portions of large curvature, local whiteout and total underexposure occur from influence of lighting and the like.
Thus, if the difference between the minimum value and the maximum value of the light intensity (light energy that enters per unit time) radiated from the same target exceeds the range of the dynamic range of the imaging element, the entire target cannot be appropriately imaged.
A technique of enlarging the dynamic range by imaging the same target over plural times under different exposure conditions, and synthesizing a plurality of images obtained thereby is known. Such a process is also referred to as a high dynamic synthesizing process or super latitude process (Super Latitude process). For instance, Japanese Unexamined Patent Publication No. 2002-334326 discloses a visual sensor that realizes enlargement of the dynamic range with small calculation processing load.